Method for annulus spacer detection in nuclear reactors

ABSTRACT

The present invention provides an apparatus for detecting and/or repositioning annulus spacers used to maintain the position of a pressure tube within a calandria tube of a nuclear reactor. The method comprises the steps of: vibrationally isolating a section of the pressure tube; vibrating the wall of said pressure tube within said isolated section; detecting vibration of the wall at a minimum of two axial positions within said isolated sections; and detecting the reduction in vibration level of the wall at one or more of said axial positions in comparison to the remaining axial positions. The apparatus comprises a tool head to be inserted into the pressure tube, the tool head comprising a first end and a second and a clamping block m each of said ends. The clamping blocks are used to vibrationally isolate a section of the pressure tube located between said ends. The apparatus also comprises piezo-actuators operable to vibrate said pressure tube; and accelerometers used for measuring vibration of said pressure tube.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/827,213, filed Aug. 14, 2015, which is a divisional of U.S. patentapplication Ser. No. 12/677,465, filed May 11, 2010, which issued onAug. 18, 2015 as U.S. Pat. No. 9,109,722, which is the U.S. NationalStage of International Application No. PCT/CA2008/001601, filed Sep. 10,2008, which in turn claims the benefit of U.S. Provisional applicationNo. 60/971,423, filed Sep. 11, 2007. Each of these applications isincorporated by reference in its entirety herein.

FIELD OF THE INVENTION

This invention relates generally to a method of repositioning annularelements (spacers) that are constrained to move longitudinally inrelation to a tube with which they are associated, the spacers beinglocated on one side of the tube wall such that they are not directlyaccessible by mechanical repositioning means.

BACKGROUND

The present invention is especially applicable to the repositioning ofspacers in a nuclear reactor, such as a CANDU® reactor. In a CANDU®nuclear reactor, the pressure tubes which contain the fuel bundles areeach positioned within a calandria tube. It is necessary to have anannular space maintained between the pressure tube and the calandriatube to allow for the circulation of gases which thermally insulate thehot pressure tube from the relatively colder calandria tube and theheavy water moderator which flows in the space outside the calandriatube.

The annular space is maintained by annulus spacers, which are onecomponent that make up a CANDU® reactor fuel channel. These spacersmaintain the radial spacing between two coaxial tubes, an inner pressuretube and an outer calandria tube, and help the calandria tubes supportthe inner pressure tubes. There are both loose-fitting and snugfittingannulus spacers, which differ in design.

A loose-fitting spacer comprises a closely coiled spring made from asquare cross section wire, assembled on a circular girdle wire to form atorus. The girdle wire of the loose-fitting spacer is welded to form acontinuous loop of fixed size. The minor diameter of the loose-fittingspacer is such that it is slightly larger than that of the outsidediameter of a pressure tube. As such, the spacer fits loosely around thepressure tube. The spacer stays in its installed position by frictionalone and not by spring tension. Loose-fitting spacers were used inearlier CANDU® reactors.

A snug-fitting spacer comprises a closely coiled spring made from asquare cross section wire, assembled on a circular girdle wire to form atorus. The girdle wire is not welded, therefore the effective minordiameter of the spacer can be increased by applying tension to extendthe coiled spring. The design of the snug-fitting spacer is such thatthe coil spring is under some tension when installed on a pressure tube,resulting in a snug fit. The design of the annulus spacer is such thatthey are not fixed rigidly in position. The spacer is held in positionby spring tension and friction. Snug fitting spacers typically maintaintheir initial desired position, however, it may be possible that aspacer may move from its desired position, or, during the course ofoperation of a reactor, it may be desirable to move the position of aspacer.

Typically, four spacers are used in a fuel channel, each spacer beingpositioned at a different axial position. To provide the requiredsupport, the annulus spacers must be located at the proper position; ifa spacer is out of position, the hot pressure tube may come into contactwith the cooler calandria tube. Such contact between the inner pressuretube and the outer calandria tube is unacceptable.

During installation of spacers in such a reactor, or, as suggestedabove, during its operation, spacers may be displaced from theirrequired positions with the result that the pressure tubes will lack thenecessary configuration of supports to carry the distributed load inoperation of the reactor, and serious problems may arise from sagging ofthese tubes. It is therefore desirable to have some way of detecting andrepositioning (if necessary) the spacers after installation or evenafter the reactor has been operating for some time. The optimal positionof a spacer may change slightly during the operating life of a reactor.The original installed spacer position is based on the supportconditions throughout the reactor life. However, it may be desirable toreposition the spacers late in the reactor life to better suit the endof life conditions. Repositioning spacers late in life may extend theoperating life of a reactor by some years, resulting in a significanteconomic benefit.

These annulus spacers are located between the pressure tubes and thecalandria tubes and are not directly accessible by mechanical means.Since the spacer position is not fixed mechanically, it is desirable tohave a means to detect their position.

U.S. Pat. No. 4,613,477 (“U.S. '477) discloses a method forrepositioning garter springs, used as annulus spacers between thecoolant tubes and calandria tubes of fluid cooled nuclear reactors. Suchgarter springs are not directly accessible by mechanical means. In themethod of U.S. '477, an electromagnetic coil is advanced along theselected fuel channel to a position adjacent the garter spring, and acurrent pulse is passed through the coil thereby to exert anelectromagnetic repulsive force on the garter spring having a componentin the direction of the required displacement. This technique isapplicable to the loose-fitting spacers which have the welded girdlewire. The welded girdle wire of the loose-fitting spacer forms acontinuous electrical circuit that is necessary for theelectromagnetic-based technique. The electromagnetic technique does notwork on the tight-fitting spacer, because the non-welded girdle wiredoes not provide a continuous electrical path within the spacer.

A need remains for an apparatus and method for detecting andrepositioning tight-fitting annulus spacers.

This background information is provided for the purpose of making knowninformation believed by the applicant to be of possible relevance to thepresent invention. No admission is necessarily intended, nor should beconstrued, that any of the preceding information constitutes prior artagainst the present invention.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, there isprovided a method of detecting an annulus spacer having an innercylindrical surface in contact with an inner tube and an outercylindrical surface in contact with a generally coaxial outer tube,which method comprises the steps of: vibrationally isolating a sectionof the inner tube; vibrating the wall of said inner tube within saidisolated section; measuring vibration in the wall at a minimum of twoaxial positions within said isolated section, and detecting a reductionin the vibration level of the wall at one or more of said axialpositions in comparison to the remaining axial position(s), wherein thereduction in vibration is indicative of the presence of the annulusspacer at or near the axial position at which said reduction invibration was detected.

In accordance with another aspect of the present inventions, there isprovided a method of axially repositioning an annulus spacer having aninner cylindrical surface in contact with an inner tube and an outercylindrical surface in contact with a generally coaxial outer tube,which method comprises the steps of: vibrationally isolating a sectionof the wall of the inner tube adjacent to the annulus spacer; causingsaid annulus spacer to go from a loaded condition to an unloadedcondition such that it is only in contact with said inner tube;vibrating the annulus spacer by vibrating the isolated section of thewall at a desired frequency such that the annulus spacer is displacedlongitudinally from an initial position to a required position, wherebythe vibration of the annulus spacer produces accelerations sufficient toovercome the tension of the annulus spacer on the inner tube.

In accordance with another aspect of the present invention there isprovided an apparatus for detecting and/or repositioning an annulusspacer having an inner cylindrical surface in contact with an inner tubeand an outer cylindrical surface in contact with a generally coaxialouter tube, comprising: a tool head having a first end and a second end;a first and a second clamping block assembly at said first and secondends, respectively, of said tool head; one or more piezo-actuatorsassociated with said tool head and operable to vibrate said inner tube;and two or more accelerometers associated with said tool head formeasuring vibration of said inner tube.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 depicts an arrangement of an inner pressure tube, an outercalandria tube and an annulus spacer.

FIG. 2 is a schematic of a CANDU® reactor showing key components,including fuel channel annulus spacers, inner pressure tubes and outercalandria tubes.

FIG. 3A depicts a tool head according to one embodiment of the presentapplication and FIG. 3B depicts the tool head of FIG. 3A positionedwithin an inner pressure tube.

FIG. 4 depicts simplified views showing the difference in mode shapesfor a pressure tube, with and without the presence of a loaded annulusspacer—View A—beam mode for circular cross-section—View B—beam mode forcircular cross-section ‘modified’ by presence of reactionary force fromannulus spacer.

FIG. 5 depicts axial variation of modes for a clamped-clamped beam. Thearrows indicate the direction of spacer movement (away from an anti-nodeand towards a node).

FIG. 6 is a plot of circumferential and axial nodal patterns for aclamped-clamped beam with a circular cross-section.

FIG. 7 shows a plot of the frequency response function for a 800 mmsection of pressure tube versus frequency, illustrating the differencesin response when there is no calandria tube/pressure tube contact (noloaded annulus spacer) and when there is calandria tube/pressure tubecontact through a spacer (loaded annulus spacer).

FIG. 8 shows a plot of frequency response ratio versus axial position ofa spacer for a frequency range around the (1,1) mode. The annulus spaceris positioned at 450 mm along the pressure tube. The plot clearly showsthat the frequency response ratio exhibits a local minima correspondingto the loaded spacer position.

FIG. 9 shows a plot of frequency response ratio versus axial position ofa spacer for a frequency range around the (2,1) mode. The annulus spaceris positioned at 450 mm along the pressure tube. The plot clearly showsthat the frequency response ratio exhibits a local minima correspondingto the loaded spacer position.

FIG. 10 shows a plot of accelerometer response to a single impactbetween an annulus spacer and a pressure tube versus time. Accelerometer3 was positioned closest to the spacer and Accelerometer 1 waspositioned furthest from the spacer.

DETAILED DESCRIPTION OF THE INVENTION

The apparatus and methods of the present invention are useful fordetection and/or repositioning of one or more annulus spacerssurrounding a first tube that is positioned within, and generallycoaxial with, a second tube (e.g., see FIG. 1). In the example depictedin FIG. 1, the annulus spacer maintains the radial spacing between thefirst tube (e.g., an inner tube) and the second tube (e.g., an outertube). Typically more than one annulus spacer work together to maintainthe radial spacing between the first tube and the second tube.

In a specific example of the present invention, the inner tube is apressure tube, the outer tube is a calandria tube and the spacer is asnug-fitting annulus spacer, as would be found in a CANDU® nuclearreactor. In another specific example, the spacer is a loose-fittingannulus spacer. As will be readily appreciated by the skilled worker,the apparatus and methods of the present application can be used inother applications in which an inner tube is positioned within andcoaxial with an outer tube and the tubes maintained in spaced relationby one or more annulus spacers.

As will be described in more detail below, there is provided anapparatus and method for detecting an annulus spacer, repositioning anannulus spacer or detecting and repositioning an annulus spacer. Themethods are based on the use of an apparatus, such as a tool head, thatis inserted inside a pressure tube.

In the case of a nuclear reactor, such as a CANDU® reactor, theapparatus (tool head) is inserted in a pressure tube when the reactor isshut down. FIG. 2 depicts an example of an arrangement of componentswithin a CANDU® reactor. The apparatus (tool head) is delivered into thepressure tube using standard, existing delivery machines. The deliverymachine is positioned at one end of the fuel channel and can form asealed connection with the fuel channel end. The delivery machine isable to remove the closure plug from the end of the fuel channel toallow access to the pressure tube. The delivery machine can introducetooling into a CANDU® fuel channel and position it at any length alongthe fuel channel. The delivery machine provides a mechanical interfacefor positioning the tool and provides for service connections to thetool, such as electrical power, control/feedback signals, pneumaticsupply, or hydraulic supply. An example of a suitable delivery machineis the AECL Fuel Channel Inspection System.

Tool Head

Referring now to FIGS. 3A and 3B, tool head 100 is sized for insertionwithin a first tube, such as pressure tube 200 in a nuclear reactor, andcomprises actuators and sensors used for annulus spacer detection,repositioning, and detection/repositioning. Tool head 100 is configuredfor operative association with a delivery machine (not shown), and issuitable for use in a wet environment as would be present in pressuretube 200 and outer calandria tube 400, for example, in a CANDU® reactor.

Tool head 100 comprises clamping block assembly 2, coupling 16,piezo-actuator 6, accelerometer 8 and eddy current gap probe 10.

Clamping Block Assembly.

As shown in FIGS. 3A and 3B, tool head 100 includes clamping blockassemblies 2 at a first end and at a second end of tool head 100. Eachclamping block assembly 2 is removably attachable to coupling 16, and isadapted for rotation about coupling 16. Each clamping block assembly 2includes clamping member(s) 20, which are moveable from a retractedposition to an extended position. In the retracted position, clampingmember(s) 20 do not impede movement of tool head 100 within pressuretube 200. In the extended position, clamping member(s) 20 engage theinner surface of pressure tube 200. Desirably, clamping member(s) 20 donot damage, or do not damage beyond acceptable tolerances, the innersurface of pressure tube 200. Each clamping block assembly 2 andclamping member(s) 20 are operable for use in pressure tube jacking(discussed further below) and are also used to vibrationally isolate asection of pressure tube 200 between each clamping block assembly 2 atthe first and second end of pressure tube 200 (discussed further below).

Coupling 16 is actuated by hydraulic pressure supplied from the deliverymachine. Actuation of the coupling 16 produces a moment between clampingblock assembly 2 and the tool head 100. When clamping block assembly 2is clamped to pressure tube 200 and coupling 16 is actuated, the momentis applied to pressure tube 200. This moment applied to pressure tube200 effectively lifts pressure tube 200 away from calandria tube 400.This operation may be used to remove any load on an annulus spacer 12and cause annulus spacer 12 to come out of contact with calandria tube400. Removal of the load from an annulus spacer 12 is required in orderto allow the annulus spacer 12 to be freely moved.

Piezo-Actuator.

Tool head 100 includes piezo-actuator 6, which is operable to applyvibrations to the inside surface of pressure tube 200. Typically onlyone piezo-actuator 6 is included in a tool head. However, more than onepiezo-actuator 6 can be incorporated in tool head 100 if desired and/orif necessary.

Piezo-actuator 6 includes bearing pad 22 that is movable from aretracted position to an extended position. In the retracted position,bearing pad 22 does not impede movement of tool head 100 within pressuretube 200. In the extended position, bearing pad 22 is brought intocontact with the inner wall of pressure tube 200.

The position of piezo-actuator 6 with respect to the clamping blockassembly 2 affects the ability of the piezo-actuator 6 to provide powerto vibrate the pressure tube in the desired mode. Piezo-actuator 6 haslimitations with respect to its travel (or stroke) and the force that itcan apply. The amount of force and stroke required to vibrate pressuretube 200 is dependent on the location of piezo-actuator 6 with respectto the mode shape, and therefore, also with respect to the clampingblock assemblies 2, which define the length of the segment of thevibrating pressure tube, and thereby affect the modes of vibration.There is a location or a location range that allows piezo-actuator 6 tobetter produce the desired mode shape or shapes. In general, a balancehas to be achieved between force and stroke. Typically, a location thatrequires less stroke also requires more force, and vice versa. Theperformance characteristics of piezo-actuator 6 is matched to the forceand stroke requirements of the particular mode shape or shapes.

When bearing pad 22 is in contact with the inner wall of pressure tube200, piezo-actuator 6 is operable to vibrate a portion of pressure tube200 in a controlled manner. Piezo-actuator 6 is controlled using anamplifier (not shown) and signal generator (not shown), such that it canbe made to operate at a desired frequency. The frequency of vibration ofpiezo-actuator 6 selected will depend on a variety of non-limitingfactors such as operating conditions, materials used, user preference,regulatory requirements and/or the like. In one embodiment,piezo-actuator 6 generates vibrations at a natural frequency of pressuretube 200. In one embodiment, piezo-actuator 6 generates vibrations inthe frequency range of about 100 Hz to about 1500 Hz. In one embodiment,piezo-actuator 6 generates vibrations at approximately 400 Hz, whichcorresponds to the (1,1) mode. In one embodiment, piezo-actuator 6generates vibrations at approximately 625 Hz, which corresponds to the(2,1) mode. In one embodiment of the invention, piezo-actuator 6generates vibrations at approximately 1096 Hz, which corresponds to the(3,1) mode.

As noted above, each clamping block assembly 2 and assembly clampingmembers 20 are operable to vibrationally isolate the section of pressuretube 200 between each clamping block assembly 2, at the first and secondends of pressure tube 200. Prior to actuation of piezo-actuator 6,assembly clamping members 20 may be moved to the extended position,contacting the inner surface of pressure tube 200. When assembly members20 are in the extended position, the portion of pressure tube 200between each clamping block assembly 2 is vibrationally isolated fromthe remainder of pressure tube 200. As used herein, vibrationallyisolated is understood to mean that vibrations produced bypiezo-actuator 6 within the portion of pressure tube 200 bounded byclamping members 20, are kept apart or away from the remainder ofpressure tube 200 so as to minimize or eliminate the effect ofvibrations on the remainder of pressure tube 200.

Accelerometers.

Tool head 100 includes accelerometers 8, which detect vibrations ofpressure tube 200. Accelerometer(s) 8 may also be used to detect impactsbetween annulus spacer 12 and the outer surface of pressure tube 200during movement of annulus spacer 12 (discussed further below).

The number and positioning of accelerometer(s) 8 in tool head 100 varywith the intended use. The accelerometers are typically used in pairs,with a pair consisting of two accelerometers 8 located at generally thesame axial position in the tool, with one accelerometer 8 positioned tomeasure acceleration at the vertical top of the pressure tube 200 andone accelerometer 8 positioned to measure acceleration at the verticalbottom of the pressure tube 200.

There are typically at least six accelerometers 8 (i.e. threeaccelerometer pairs), however, additional accelerometer 8 pairs may beused. Desirably, tool head 100 includes twelve accelerometers 8 mountedas six pairs. In the embodiment of FIG. 3A, tool head 100 includestwelve accelerometers 8. The embodiment of FIGS. 3A and 3B provide threeaccelerometer 8 pairs on either side of the axial centreline of thetool, allowing the tool head to measure the position of annulus spacer12 on either side of the tool head centre, which corresponds to theantinode locations for j=2 modes. In other embodiments, there are onlysix accelerometers 8 (three pairs) located on one side of the tool axialcentre. In a specific embodiment of the invention, the tool incorporatesmeans for moving the accelerometers axially within the tool to improvethe detection resolution. This may be accomplished by mountingaccelerometers 8 in a moveably attached component within tool head 100which may be moved axially within tool head 100 by any standardmechanical means such as an electric motor and leadscrew or a hydrauliccylinder.

Eddy Current Gap Measurement Probe.

Tool head 100 also includes eddy current gap measurement probe 10 toobtain measurements to confirm that annulus spacer 12 is in the unloadedposition following pressure tube jacking. Such use of eddy current gapmeasurement probe 10 is known to the skilled worker. In the embodimentof FIGS. 3A and 3B, tool head 100 includes two eddy current gap probes10 to enable the gap above and below the pressure tube 200 to bemeasured simultaneously. In other embodiments, there is only one eddycurrent gap probe 10 to measure the gap below the pressure tube. In aspecific embodiment of the invention, tool head 100 includes three eddycurrent gap probes 10 to measure the gap above, below, and to one sideof the pressure tube.

Umbilical

Tool head 100 is configured for operative association with umbilical 30.Umbilical 30 includes appropriate electrical cables and hydraulic and/orpneumatic hoses to connect tool head 100 to an out-of-reactor power unitand control system (not shown). Out-of-reactor power unit includes ahydraulic power supply (pump, valves) and electrical power supplies.This unit is a source of power and amplification, and may be positionedadjacent to the reactor, proximal to the services for the deliverymachine.

Control Station.

Tool head 100 is operable from a control station (not shown), which isdesirably located in a low radiation environment, away from the reactor.The control station includes such items as signal conditioning fortransducers, means for data acquisition and an operator interface.Special purpose software is included to control tool head 100 andanalyse the data resulting from annulus spacer 12 detection, movementand/or detection and movement processes. Dedicated procedures, outlinedfor example in user manuals, are included to guide/instruct operators inannulus spacer 12 detection and/or annulus spacer 12 repositioning. Itwill be clear that tool head 100 can be included as a kit, to retrofitexisting machines.

Methods

During operation of a reactor, it may be possible for annulus spacer(s)12 to move axially along pressure tube 200. This movement of annulusspacer(s) 12 can result from vibration and/or thermal cycling of thereactor. When axial movement of annulus spacer(s) 12 occurs, it may benecessary or desirable to reposition annulus spacer(s) 12. Alternativelyor additionally, it is possible that initial placement of annulusspacer(s) 12 is not optimal or desired, and here again it may benecessary or desirable to reposition annulus spacer(s) 12, from a firstposition to a second position.

Tool head 100 may be used for (i) detecting annulus spacer(s) 12, (ii)repositioning annulus spacer 12, and/or (iii) detecting annulus spacer12 during repositioning. Vibration-based techniques are used for bothdetection and repositioning of annulus spacer 12. The followingdiscussion provides details of methods of using the apparatus of thepresent invention to detect and/or reposition an annulus spacer;however, it will be clear that variations can be made to the followingmethods while not deviating from the present invention. Such methods arewithin the scope of the present application.

Annulus Spacer Detection

Detection of annulus spacer 12 is achieved by monitoring changes in theresponse of the pressure tube 200 vibrations caused by the presence ofannulus spacer 12.

Tool head 100 is inserted in pressure tube 200 to an initial position.The initial position may be close to a position where a user expectsannulus spacer 12 to be. Alternatively, if for example the user does nothave knowledge of where annulus spacer 12 is anticipated to be, theinitial position of tool head 100 can be an arbitrary position withinpressure tube 200.

After the tool head is positioned at the selected location, clampingmembers 20 are actuated to move into contact with and apply pressure tothe wall of the inner tube in such a manner that a section of the innertube is vibrationally isolated from the remainder of the tube. Thevibrational isolation is used to establish a consistent environment fordetection of changes without effecting the remainder of the tube. Theisolated section is subsequently vibrated through the action of thepiezo-actuator and acceleration measurements are taken at three or moreaxial locations to determine the frequency response. The measurementsfrom the different axial locations are compared and a relative change inthe frequency response indicates the presence of a loaded spacer.

FIG. 5 depicts plots of the first and second axial mode shapes for aclamped-clamped beam. As used herein, “clamped-clamped beam” can beestablished with tool head 100 positioned in the desired location ofpressure tube 200, each clamping block assembly 2 is actuated to moveassembly clamping member 20 from the retracted position to the extendedposition, thereby vibrationally isolating a portion of pressure tube200.

FIG. 6 depicts the circumferential and axial mode shapes for aclamped-clamped beam with a circular cross-section.

Detection of the position of annulus spacer 12 is based on thedifferences in the vibration responses at the top and bottom of pressuretube 200 vibrating in the vicinity of a loaded annulus spacer 12.Annulus spacer 12 primarily contacts calandria tube 400 near the bottomof the tube, and transmits force to the pressure tube 200 primarily atthis location. Detection is achieved by exciting a random vibration inpressure tube 200 using piezo-actuator 6 and measuring the response ofpressure tube 200 at both a top position and a bottom position ofpressure tube 200 using accelerometers 8 at three or more axiallocations. The acceleration is monitored at the natural frequencies ofthe pressure tube section, where the expected maximum accelerations arehighest. The presence of annulus spacer 12 alters the local accelerationand deflection of the pressure tube wall, primarily at the bottom ofpressure tube 200. This produces an asymmetry in the circumferentialmode shape. In use, tool head 100 is positioned inside pressure tube 200and random vibrations are excited using tool piezo-actuator 6.

A comparison between the pressure tube acceleration at the top positionand the bottom position is performed at multiple axial positions toidentify spacer location(s). This is illustrated in the views providedin FIG. 4. View A depicts a simplified axial cross section view of abeam mode in a pressure tube. Acceleration measurements are taken at thetop position and the bottom position, designated a_(t) and a_(b),respectively, in FIG. 4. View B shows a simplified view of the‘modified’ beam mode as it is affected by the reactionary force from aloaded annulus spacer 12. The presence of annulus spacer 12 isdetermined by comparing measurement a_(t) and a_(b) at various axiallocations along pressure tube 200. In the absence of annulus spacer 12,the absolute value of a_(t) and a_(b) are approximately equal. However,when a loaded annulus spacer 12 is present, there is a differencebetween a_(t) and a_(b). The value of a_(b) is reduced typically in therange of 20-40% compared to the value of a_(t). At any given frequency,the ratio of the absolute value of the acceleration measured at the topand bottom of the pressure tube is defined as the frequency responsefunction at that frequency.

FIG. 7 depicts a plot of the frequency response function spectra for asection of pressure tube, with and without the presence of a loadedannulus spacer. The plot of FIG. 7 shows that there are significantdifferences in the frequency response function with and without a loadedspacer in certain frequency ranges. This relationship allows spacerdetection to be achieved by analyzing the accelerations within anidentified frequency range or ranges.

FIG. 8 is a plot depicting the frequency response ratio as a function ofaxial position along the pressure tube for frequencies in the range ofthe (1,1) mode. The loaded annulus spacer is located at the 450 mm axialposition of a 800 mm long pressure tube section. The testing was donewith an annulus spacer load of 400 N. The plotted frequency responsefunction exhibits a minima of approximately 0.6 at the axial locationcorresponding to the annulus spacer.

FIG. 9 depicts a plot of the frequency response ratio as a function ofaxial position along the pressure tube for frequencies in the range ofthe (2,1) mode. The loaded annulus spacer is located at the 450 mm axialposition. The plotted frequency response function exhibits a minima ofapproximately 0.76 at the axial location corresponding to the annulusspacer.

Pressure Tube Jacking

After some period of operation of a reactor, annulus spacer 12 is incontact with pressure tube 200 and outer calandria tube 400 (a loadedcondition). For repositioning of annulus spacer 12, it is necessary tobring annulus spacer 12 out of contact with calandria tube 400 (anunloaded condition), to free annulus spacer 12 for movement. Movingannulus spacer 12 from a loaded condition to an unloaded condition iscarried out by applying a moment of force to pressure tube 200 usingtool head 100. This procedure is also known to the skilled worker aspressure tube jacking or jacking. Eddy current gap probe(s) 10 is/areused to measure the pressure tube-to-calandria tube gap, to confirm thatannulus spacer 12 is in the unloaded condition. Thus, eddy current gapprobe(s) 10 may also be used to determine if it is necessary to apply amoment of force to pressure tube 200.

Tool head 100 is configured to apply a moment of force to pressure tube200, using clamping block assembly 2. As noted above, clamping blockassembly 2 is operable for rotation about coupling 16. To apply a momentof force, tool head 100 is positioned within pressure tube 200 andassembly members 20 are moved to the extended position. Each clampingblock assembly 2 is rotated (in opposite direction to one another) and amoment of force is applied in the vertical plane parallel to thepressure tube axis. The applied moment of force effectively lifts innerpressure tube 200 off outer calandria tube 400, thereby taking annulusspacer 12 out of contact with calandria tube 400 and freeing annulusspacer 12 for movement. Thus, by applying the moment of force topressure tube 200, annulus spacer 12 is moved from the loaded conditionto the unloaded condition. Such pressure tube jacking is also used inthe case of a type of annulus spacer known as a loose-fit spacer.

Annulus Spacer Repositioning

Repositioning of annulus spacer 12 is achieved by vibrating a section ofthe pressure tube in a controlled manner. To reposition annulus spacer12, tool head 100 is positioned within pressure tube 200 at a desiredlocation with respect to annulus spacer 12. Desirably, the position ofannulus spacer 12 is determined as discussed above. Once tool head 100is positioned in the desired location, each clamping block assembly 2 isactuated to move assembly clamping member 20 from the retracted positionto the extended position, thereby vibrationally isolating a portion ofpressure tube 200. This vibrational isolation provides a standard fixedlength of pressure tube 200 located between the two clamping blockassemblies 20 for the vibration-based repositioning of annulus spacer12. Tool head 100 is used to apply a moment of force to pressure tube200, to raise the pressure tube and remove the load from the annulusspacer 12. In some instances, if the annulus spacer were normally in theunloaded condition, it is possible to move a snug-fitting annulus spacer12 without jacking the pressure tube. The unloading of annulus spacer 12is confirmed by measuring the pressure tube-to-calandria tube gap usingeddy current gap probe 10. Eddy current gap probe 10 providesinformation used to determine the amount of moment necessary to apply topressure tube 200.

Once in position, and annulus spacer 12 is in the unloaded position,bearing pad 22 within piezo-actuator 6 is moved from the retractedposition to the extended position. Piezo-actuator 6 is operable tovibrate the pressure tube 200 at the desired frequency. The frequency ofvibration is selected to match a natural frequency of the isolatedpressure tube section. Typically the (2,1) mode is used for spacerrepositioning as this mode provides for the highest efficiency in termsof power provided by the piezo-actuator versus peak pressure tubeacceleration produced. However, other higher modes such as (2,2) and(2,3) may be used. For a water-filled pressure tube with an activevibrating length of 800 mm, frequencies of 626 Hz, 793 Hz and 1096 Hzcorrespond to the (2,1), (2,2) and (2,3) modes, respectively. Thefrequency of vibration of piezo-actuator 6 selected will depend on avariety of non-limiting factors such as operating conditions, actualpressure tube size, damping effects of the tool head, user preference,regulatory requirements and/or the like. The frequency of vibrationproduced may be adjusted to match the actual natural frequency bymonitoring the pressure tube acceleration produced during actuation. Thevibrations cause annulus spacer 12 to vibrate as well. These vibrationsin annulus spacer 12 produce accelerations that are high enough toovercome the spring tension in the spacer and allow the spacer to liftoff of the surface of the pressure tube. Desirably, tool head 100 ispositioned to initially place annulus spacer 12 between a node and ananti-node of the mode shape generated by the vibrations. The vibrationstypically cause annulus spacer 12 to move away from an anti-node andtowards a node (FIG. 4). This is shown graphically in FIG. 4, whichshows two axial mode shapes of a clamped-clamped beam. The relativeposition of annulus spacer 12 with respect to the mode shape determinesthe direction of spacer movement. A variety of mode shapes may be used.The greater the mode number desired for use, the greater the amount ofpower that is required to produce an equivalent acceleration.

Annulus Spacer Monitoring During Repositioning

In one example, the movement of annulus spacer 12 is monitored duringmovement of annulus spacer 12. This is carried out using accelerometers8 to detect the high frequency impacts between annulus spacer 12 andpressure tube 200 as annulus spacer 12 vibrates during movement.Multiple accelerometers at different positions on tool head 100 areused. The difference in the time when the impact is detected by theaccelerometers and the magnitude of the impact is used to determinespacer location and movement.

FIG. 10 is a graph depicting acceleration as a function of time,detected at accelerometers 8 positioned at various positions on toolhead 100. (Each of the three accelerometers 8 is designated 1, 2, and3). The data were taken from a single annulus spacer 12 impact with thepressure tube 200. In this example, accelerometer 3 was located 27 mmaxially from the annulus spacer 12 and near the pressure tube top.Accelerometer 2 was located 76 mm axially from annulus spacer 12 andalso near the pressure tube top. Accelerometer 1 was located 87 mmaxially from annulus spacer 12 and was located near the pressure tubebottom. It will be noted from the graph that the start of theacceleration response occurred later in time the further away from theimpact accelerometer 8 was located. The wave front moves atapproximately 1700 m/s. The initial acceleration peak is reduced thefurther away the accelerometer is from the annulus spacer impact. Thetime delay and the reduction in amplitude may be used to determine theposition of annulus 12 spacer impact.

Kits

It will be clear that tool head 100, and/or components of tool head 100,can be included as a kit. Such a kit may optionally include instructionsfor use and/or software for operating tool head 100.

All publications, patents and patent applications mentioned in thisSpecification are indicative of the level of skill of those skilled inthe art to which this invention pertains and are herein incorporated byreference to the same extent as if each individual publication, patent,or patent applications was specifically and individually indicated to beincorporated by reference.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

We claim:
 1. A method of detecting an annulus spacer having an innercylindrical surface in contact with an inner tube and an outercylindrical surface in contact with a generally coaxial outer tube,which method comprises the steps of: (a) vibrationally isolating asection of the inner tube; (b) vibrating a wall of said inner tubewithin said isolated section; (c) detecting vibration of the wall at aminimum of two axial positions within said isolated section; (d)detecting a reduction in vibration level of the wall at one or more ofsaid axial positions in comparison to the remaining axial position(s),and (e) making a determination that the reduction in vibration levelindicates a presence of the annulus spacer at the axial position atwhich said reduction in vibration was detected.
 2. The method of claim1, wherein said step of vibrating the wall of said inner tube usesvibrations at a natural frequency of the inner tube.
 3. The method ofclaim 1, wherein said step of vibrationally isolating the section of theinner tube comprises applying pressure to the inner surface of the wallof the inner tube at a first and a second position, the first and secondpositions defining the boundaries of said vibrationally isolatedsection.
 4. The method of claim 3, wherein said step of vibrating thewall of said inner tube uses vibrations at a natural frequency of theinner tube.
 5. The method of claim 1, wherein said step of vibrating thewall of said inner tube uses vibrations in a frequency range of 100 Hzto 1500 Hz.
 6. The method of claim 5, wherein the vibrations are at afrequency of 400 Hz, or 625 Hz or 1096 Hz.
 7. The method of claim 1,wherein said detecting step includes calculating a frequency responseratio of the measured vibrational frequency at the top and bottom ofsaid inner tube at each of said one or more axial positions.
 8. Themethod of claim 7, wherein said step of vibrationally isolating thesection of the inner tube comprises applying pressure to the innersurface of the wall of the inner tube at a first and a second position,the first and second positions defining the boundaries of saidvibrationally isolated section.
 9. The method of claim 8, wherein saiddetecting step further includes detecting a decrease in the frequencyresponse ratio and making a determination that said decrease in thefrequency response ratio indicates the presence of the annulus spacer atthe axial position at which said decrease in the frequency responseratio was detected.
 10. The method of claim 7, wherein said detectingstep further includes detecting a decrease in the frequency responseratio and wherein said decrease in the frequency response ratio isindicative of the presence of the annulus spacer at the axial positionat which said decrease in the frequency response ratio was detected.